1. Field of the Invention
The present invention relates to improvements in the use of a high-performance, catalytically activated carbon for the removal of chloramines from chloramine-containing fluid streams. In particular, this application relates to the use of high-performance, catalytically activated carbon block filters for the removal of chloramines from chloramine-containing fluid streams.
2. Description of the Prior Art
While chlorination has made the U.S. water supply safe from illness producing bacteria, viruses, and parasites, an unhealthy by-product of chlorinating water that contains natural organics is the production of trihalomethanes, which have been linked to increased risk of cancer. One way to reduce this risk is to change from chlorine disinfection to chloramine disinfection. Chloramines are formed from the reaction between ammonia and chlorine. Thus, adding ammonia (NH3) to a chlorination system converts chlorine to chloramines. Specifically, monochloramine, hereafter referred to as xe2x80x9cchloramine,xe2x80x9d in low concentrations arise from the disinfection of potable water sources. To improve the taste and odor of the water and to remove the inherently toxic chloramine, the water is typically contacted with activated carbon. The ability of carbonaceous materials, such as activated carbon, to remove chloramine from aqueous streams is generally well known. It is also known that improvements in removal of chloramine can be achieved by reducing the mean particle diameter of the carbon and by increasing the carbon bed contact time. In some applications, such as in kidney dialysis units, high removal rates of chloramine are particularly important. Although parameters such as contact time and mean particle diameter are known to affect chloramine removal efficiencies, removal performance is neither well understood nor particularly effective.
Activated carbon is used in the treatment of water in the form of powdered actvated carbon, granular activated carbon, or shaped activated carbon, such as pellets or spheres. Another form of shaped activated carbon often recommended for point-of-use (POU) and point-of-entry (POE) water treatment, however, is solid block activated carbon. Block activated carbon is a compressed blend of selected activated carbon and a binder material, such as high-density polyethylene (HDPE), which is capable of adsorbing a wide range of organic materials. Water is forced through the pores of the densely compacted carbon block, where a combination of mechanical filtration, electrokinetic adsorption, and physical/chemical adsorption takes place to reduce or eliminate a wide range of contaminants.
U.S. Pat. No. 5,338,458, issued on Aug. 16, 1994 to Carrubba et al., titled xe2x80x9cMethod for Removing Chloramine with Catalytic Carbon,xe2x80x9d teaches an improved process for the removal of chloramine from gas or liquid media by contacting said media with a catalytically-active carbonaceous char. In practice, however, a product manufactured according to the patent teaching has been found lacking in effectiveness for chloramine removal from drinking water. Additionally, attempts to replicate even the relatively poor performance of the commercial product based on the ""458 patent (Centaur(copyright)) in solid block form has not been satisfactory. Apparently, the impact of the binder component detracts measurably from the prior art carbbn""s performance for chloramine removal.
Accordingly, it is the object of the present invention to provide an improved method of removal of chloramine from drinking water. It is a further object of the invention to provide an activated carbon that is catalytically active for removal of chloramine apart from factors such as extended contact time, mean particle diameter, and the like which factors are known to affect removal of chloramine. Finally, it is an object of this invention to provide an improved method of chloramine removal using an activated carbon that is catalytically active for removal of chloramine in the form of a solid block activated carbon.
Generally, the present invention comprises a method for enhanced removal of chloramine from aqueous media by contacting said media with a catalytic activated carbon. The catalytic activated carbons used in the present invention may be prepared from carbon materials that have been contacted or otherwise exposed to nitrogen-containing compounds at temperatures above 700xc2x0 C.
The carbonaceous feedstocks from which such carbons are produced are relatively nitrogen-poor, naturally occurring materials, such as lignocellulosic materials and coals. The lignocellulosic materials may include carbons derived from wood, olive pits, and various nut shells, including coconut. The nitrogen-poor feedstocks may be processed as low-temperature carbonized chars or as high-temperature carbonized chars such as activated carbons. Either carbon may be oxidized prior to, during, or after carbonization. However, all nitrogen-poor chars must be contacted or otherwise exposed to nitrogen-containing compounds such as ammonia, urea or the like at high temperatures prior to, during, or after calcination, pyrolysis, and/or activation at high temperatures with a gasifying agent, such as steam or carbon dioxide. Additionally, it is essential that the final products in all cases described above be cooled to temperatures below 400xc2x0 C., preferably 200xc2x0 C., in an oxygen-free or otherwise inert atmosphere. In the invention of a block carbon, after treating the carbon it is blended with a binder material and the blend is shaped to a desired forrn. In a preferred embodiment, the binder material is an organic compound, such as a polymer, which has been heated to a temperature at least above its glass transition temperature (preferably, above its melting point), and the blend is shaped as desired prior to resolidification of the binder. Alternatively, the binder material may also be inorganic, such as one or more clays.
The catalytic activated carbons of the present invention are distinguished from prior art carbons by their ability to extract a greater amount chloramine from drinking water more rapidly. When tested under nearly equivalent conditions of contact time, mean particle diameter, concentration of chloramine, and the like, these catalytic activated carbons remove chloramine much more effectively than prior art carbon materials, which have been used for this application in the past, including the carbonaceous chars of U.S. Pat No. 5,338,458. Other advantages of the present invention will become apparent from a perusal of the detailed description of the presently preferred embodiments.